Tagged Questions

This tag is for questions about the quantum mechanical measurement problem, such as e.g. the wavefunction collapse/decoherence. DO NOT USE THIS TAG for non-quantum measurements.

106 views

Can the Born rule be derived? [duplicate]

$\renewcommand{ket}[1]{|#1\rangle}$ If we have a particle and we know the initial state $|\psi\rangle$ of everything that is relevant, and we know the full Hamiltonian $H$, then we should be able to ...
240 views

How does one describe a state with a density matrix after measuring position?

My question is about position measurement in non relativistic quantum mechanics. I've been taught that when you measure the value of an observable for some state of a system described by $|\psi\rangle$...
158 views

Weak measurement and weak value

The concept of weak measurements (and weak values) have become popular in Quantum information community, as I can see quite a few papers in arXiv. Since I am from Mathematical background (and the ...
104 views

Can I measure distance with sound through soil?

Can you measure distance (cca. with precision 0.1m-1m) with sound through soil. I know this is really crazy think to do, but I have this idea quite for a while. Basically I will set speakers on fix ...
43 views

ideally accurate measurement

In the address below http://en.wikipedia.org/wiki/Measurement_in_quantum_mechanics it's written: For pedagogic reasons, the measurement [in quantum mechanics] is usually assumed to be ideally ...
163 views

Momentum uncertainty of free particle

I've read several Q&A's regarding free particles and the associated wave packet in this website, but found the answer to my question nowhere. It's OK to attribute a Gaussian wave packet to the ...
199 views

Does measurement change the evolution of wave function?

Basically any measurement is on wave function $|\psi\rangle$ is done by operator $X$ such that $X|\psi\rangle$ results observable $x$ with some probability. But what happens to $|\psi\rangle$? Does ...
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Quantum computing can be done via measurement alone, why is this significant?

I read in the Afterword section of Nielsen and Chuang's book Quantum Computation and Quantum Information that A second area of progress has been in understanding of what physical resources are ...
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Why isn't everthing in a superposition state? [duplicate]

I know that a superposition is a state in which there are 50% and 50% (other % also) chances of two things to happen so why am I not in a superposition state? Example, I am at rest and i now choose to ...
109 views

Entanglement and the uncertainty principle

Suppose you have two maximally entangled particles. You measure the spin about the x axis of the first and the spin about the y axis of the second. But both spins cannot be known simultaneously, so ...
77 views

Compatible Observables and Measurement

Suppose $A$ and $B$ are compatible observables (i.e. $[A,B] = 0$). We take the eigenkets of $A$ to be $|a_1 \rangle \ldots |a_N \rangle$. Further, we suppose that the first $k$ eignekets of $A$ are ...
164 views

Why superpositions? [closed]

I've seen a lot of stuff on superpositions, namely the double slit experiment. And every video I watch, it tells me the same thing: It's amazing that when these particles are being observed they ...
266 views

What is the meaning of “ Ψ is not a measurable quantity in itself”?

I want to know that why the wavefunction Ψ as a complex quantity (i.e $A+iB$ form) in quantum mechanics and somewhere I have studied that Ψ is not a measurable quantity in itself that's why we ...
128 views

Physical meaning of quantum interpretations [closed]

Do interpretations of quantum mechanics have physical meaning? An argument for no would be the fact that no matter the interpretation, one gets the same measurements. They also do not follow logical ...
903 views

Double slit experiment with animals as observers

I was searching about the double slit experiment, reading and watching videos, etc. If I understood correctly, when they measure the photon it behaves like a particle. On the Youtube video Tom ...
87 views

Quantum state of a system after measurements with non-commutative operators

a) Assume two operators $A$ and $B$. 1) Assume $$[A,B]=0$$ and $$ψ= \sum c_n u_n ~~~~\text a~ wavefunction~ describing~ the~ state~ of~ the~ system$$ with $$Aψ=a_n u_n$$ $$Bψ=b_n u_n$$ If we ...
603 views

Is a photon always in a state of superposition while traveling through space?

In the double-slit experiment, we emit a photon that is in a state of superposition (wave form) which travels through both slits to interfere with itself. When we measure which slit it went through, ...